WASHINGTON (AP) — Republican Donald Trump on Sunday refused to rule out an independent bid for president in 2016, and he dug in on creating a database to track Muslims in the U.S.

Asked on ABC’s “This Week” whether he would consider a third-party run if GOP opponents try “to take you out,” Trump said, “I will see what happens. I have to be treated fairly. If I’m treated fairly, I’m fine.”

The billionaire and former reality show star is leading the race for the GOP nomination for the fourth straight month, with Republican establishment candidates such as Jeb Bush and Marco Rubio far behind. All the GOP candidates, Trump included, have signed a pledge to support the party’s eventual presidential nominee and forgo independent runs in 2016.

He suggested that his lead in the polls, unshaken by disparaging remarks he’s made about ethnic groups or his lack of specifics on foreign policy, has vexed the Republican party.

“They can’t understand, you know, how come an outsider can be doing so well within the party,” Trump said.

His standing in national polls has only solidified since recent Islamic militant attacks in Europe, particularly the Nov. 13 strikes on Paris that killed 130 people and wounded hundreds of others. The Islamic State group has claimed responsibility for those attacks. The upsurge in violence has put pressure on the candidates from outside government, primarily Trump and retired neurosurgeon Ben Carson, who have little foreign policy or national security experience.

Trump has pledged to be the toughest of all candidates toward people posing threats to the U.S. On Sunday said he would back ways to track Muslims in the U.S. and also bring back waterboarding on terrorism suspects.

“I would bring it back, yes. I would bring it back. I think waterboarding is peanuts compared to what they’d do to us,” he said.

Trump this weekend has tried to back away from his support for a government database to track Muslims in the United States, an idea that drew sharp rebukes from his GOP rivals and disbelief from legal experts. On Thursday, an NBC News reporter pressed Trump in Iowa on whether there should be a database for tracking Muslims in the U.S. Trump replied: “There should be a lot of systems, beyond databases.”

Would he put such a database in place as president?

“I would certainly implement that. Absolutely.”

He tried in another interview to clarify that position, suggesting a “watch list” for the Syrian refugees admitted to the U.S.

On ABC Sunday, Trump was asked if he rules out a database on all Muslims in the U.S.

“No, not at all,” Trump said. “I definitely want a database and other checks and balances. We want to go with watch lists. We want to go with databases.”